This invention relates to the combustion of sulfur-containing fuels, and, more particularly, to a reactor and method for reducing sulfur oxides emissions in gaseous products resulting from the combustion of sulfur containing fuels.
Substantial efforts have been made to reduce sulfur oxides emissions in gaseous products resulting from the combustion of sulfur containing fuels in reactors to comply with environmental regulations. For example, in the operation of fluidized bed reactors, limestone is often added to the fluidized bed medium, which includes crushed coal, for absorbing the sulfur oxides generated as a result of combustion of the coal. This method, however, results in excessive limestone consumption when reducing emissions of sulfur oxides beyond 90 percent.
The excessive consumption of limestone results in several undesirable effects. For example, the requirement to reduce sulfur oxides emission beyond 90 percent necessitates a Ca/S mole ratio of 3.5 or higher which results in ash which is both hazardous and expensive for disposal. Further, the excessive consumption of limestone results in a significant increase in the emission of nitrogen oxides, as well as in a substantial reduction in reactor efficiency due to an increase in limestone calcination.
More recent advances in reducing the emission of sulfur oxides rely on a dry scrubbing process in which lime is slaked to form a slurry of calcium hydroxide. The calcium hydroxide slurry is introduced into a spray dryer through an atomizer which creates a plurality of slurry particles which react with the sulfur oxides to form calcium sulfate or calcium sulfite while the slurry droplets are simultaneously dried. Typically, the dried particles and fly ash are removed from the flue gas stream by a fabric baghouse filter.
However, this dry scrubbing process is generally considered too expensive for use in many industrial coal-fired fluidized bed reactors because it incurs a significant cost disadvantage by using lime instead of limestone since the cost of the lime is as much as ten times the cost of the limestone.
Accordingly, there remains a need in the art for a method for treating flue gases to remove fly ash and to remove sulfur oxides without incurring the additional cost of using lime.